SYNTHESIS OF NITIDULID BEETLE PHEROMONES - ALKYL-BRANCHED TETRAENE HYDROCARBONS

Synthetic procedures are presented for four tetraene hydrocarbons that had been identified as pheromone components for the driedfruit beeatle, Carpophilus hemipterus (L.), or the dusky sap beetle, C. lugubris Murray (Coleoptera: Nitidulidae). These compounds are (2E,4E,6E,8E)-3,5,7-trimethyl-2,4,6,8-decatetraene, (2E4E6E8E)-3,5,7-trimethyl-2,4,6,8-undecatetraene, (2E4E6E8E)-7-ethyl-3,5-dimethyl-2,4,6,8-decatetraene, and (2E4E6E8E)-7-ethyl-3,5-dimethyl-2,4,6,8-undecatetraene. The general synthetic scheme starts with tiglic aldehyde, (E)-2-methyl-2-butenal, extends the carbon chain with two Wittig-Horner olefinations, and completes the chain with a Wittig reaction. Lithium aluminum hydride reductions and manganese dioxide partial oxidations are used to prepare the intermediates for the subsequent chain extensions. The incorporation of methyl or ethyl side chains is controlled by the choice of the Wittig-Horner reagent, triethyl 2-phosphonopropionate or triethyl 2-phosphonobutyrate, respectively. After distillation of the final products, the all-E 3,5,7-trimethyl tetraenes were produced in 83-84% purity and 40-42% overall yield and the all-E 7-ethyl-3,5-dimethyl tetraenes in 71-73% purity and 20-25% overall yield from tiglic aldehyde.